EP2067567B1 - Method for manufacturing of integrally bladed rotors for compressors and turbines - Google Patents

Description

The invention relates to a method for producing integrally constructed impellers for compressors and turbines, in particular for gas turbine engines, in which the wheels comprising a disk with blades formed on the circumference are manufactured by means of conventional shaping processes and then the thickness and chord length by chemical treatment in an etching medium the blades is reduced.

Such a method is from the EP 1 239 059 known.

In compressor and turbine technology and in particular in aircraft engines increasingly produced in one piece wheels, called BLISKS, are used. Compared to the conventional design, in which separately manufactured blades are held in a groove on the circumference of the disc, the integrally formed impellers allow higher rotational speeds due to their low mass, so that an improved pressure ratio can be achieved and thus more powerful engines are available. Furthermore, there are no leakage losses in the area of the blade root. Due to the one-piece design and rigid coupling of disc and blades Blisks are compared to disturbances of rotational symmetry, that is a detuning of the overall structure to be regarded as more sensitive. This characteristic, also known as "mistuning", of BLISK-type impellers, which is reflected in specific disk and blade properties due to the manufacturing process and material inhomogeneities, is due to aerodynamic excitations with characteristic amplitude and stress peaks in the blades and resulting therefrom . associated with the life of the wheels restricting increased fatigue.

A method has already been proposed by means of which the natural frequencies of the individual blades of a BLISK can be determined in a realistic manner in order to detect production-related disturbances in the rotational symmetry of an impeller based on the metrological determination of the blade natural frequency deviations from the average of all blade internal frequencies and to draw appropriate conclusions about the vibration behavior BLISK under operating conditions and their operational safety and service life.

From the EP 1239059 A2 A method of balancing impellers made by integral-machining machining is known in which the thickness and chord length of at least one blade are reduced by material removal in an etching solution. The amount of material removal at the blade surface is determined by the treatment time in an etching bath. If only one of a plurality of blades immersed in the etching bath is to have a reduction in thickness and thus a weight reduction for the purpose of balancing, the remaining blades are covered with a mask which is chemically resistant to the etching medium.

The invention has for its object to provide a method for producing integrally formed, produced by machining and / or electrochemical machining and / or friction welding compressor or turbine wheels for gas turbine engines, the blades have substantially matching maximum vibration amplitudes and low blade loads, so that a long life of the wheels is guaranteed.

According to the invention the object is achieved by a method according to the features of patent claim 1. Advantageous developments of the invention are the subject of the dependent claims.

The basic idea of the invention is that, after the production of the impeller by conventional shaping methods, for example by milling, the natural frequency of the blades, which is essentially determined by the blade thickness and chord length, is measured and the corresponding blade mass is calculated from the respective natural frequency. Starting from the blade of the lowest blade mass, for each remaining blade, their respective blade mass deviation from the blade with the lowest blade mass is determined and removed in an etching process from the relevant blade, so that all blades have a substantially matching blade mass and blade natural frequency, corresponding to the lowest Blade mass and natural frequency, thus, amplitude peaks and extreme blade loads can be largely avoided, so that the life of the thus manufactured impeller is increased. An additional beneficial effect of the congruent centrifugal load of all blades by reducing the blade masses of the blades to a lowest matching blade weight is also that a possible impeller unbalance is reduced because the imbalance caused by the blades is eliminated.

According to a further feature of the invention, the stiffening and Eigenfreu tuenserhöhung the provided with a strain gauge blades in a tested before series test wheel off in that during the etching treatment in the relevant blades of the test wheel, the blade thickness and the chord length corresponding to that due to the strain gauges expected to increased natural frequency is further reduced. Thus, the test result can not be falsified in test mode due to the strain gauge application.

The reduction of the blade thickness and the chord length in the respectively required size is determined by the concentration of the etchant and the duration of the action on the blade.

In a further embodiment of the invention, each blade is individually treated in a matched to the blade size, filled with the etchant container.

The impeller may be immersed in an etching bath for a separate removal of material on each individual blade, but also as a whole, if the disk and all other blades - already treated or not yet treated - are protected from the etchant by a chemically resistant masking.

In an advantageous development of the etching process, in the case of an impeller immersed completely in the etching bath, the smallest blade mass deviations of the lowest blade mass can be removed in successive etching steps. In this case, the disk is covered with a mask and before each etching step, the blade with the smallest mass or the previously treated blades whose mass is already reduced to the minimum, protected by the application of a masking agent from the action of the etchant.

In an embodiment of the invention, the determination of the natural frequency of the blades takes place in such a way that each blade is excited individually and in a reproducible size with a modal hammer and in from the other blades largely decoupled state with a laser vibrometer contactless, the respective natural frequency is measured. The decoupling of the other blades during the measurement of the natural frequency is carried out by an additional detuning of all other, not measured blades with a temporarily attached to this additional weight.

The shape of the impeller manufactured in Integralbauweise done with known machining methods, for example by milling, electrochemical machining or friction welding.

An embodiment of the invention will be explained in more detail below.

First, by conventional methods, for example by milling, for a compressor stage of a gas turbine engine, an impeller in blisk construction with integrally formed on a disc - for example 25 - blades produced. Due to the blade geometries deviating from the production and / or material inhomogeneities, the blades have different natural frequencies, so that the maximum blade amplitudes and blade voltages vary from blade to blade and the blades are loaded differently and sometimes very heavily during operation - with the consequence of a reduced service life would.

In the next step, the natural frequency of each individual blade is measured in a state largely decoupled from the other blades. For decoupling the unexamined blades are additionally detuned with an identical additional mass. Thereafter, the blade to be examined is offset with a modal hammer in a - reproducible in the study of the other blades - blade excitation and with a Laser vibrometer measured the natural frequency of the blade contactless.

die jeweiligen individuellen Schaufelmassen m _schaufel bestimmt.Once in the manner described above, the blade natural frequency f _shovel was determined for all the blades of the impeller are on the existing between the blade natural frequency and the blade mass m _shovel relationship $$m_{\mathit{shovel}}=\mathrm{f}\left(f_{\mathit{shovel}}\right)$$

the respective individual blade masses m _scoop determined.

errechnet.On the basis of the lowest blade mass determined by all the blades investigated, that is, the blade having the lowest natural frequency and accordingly the lowest blade mass m _{shovel min} as the reference variable, the mass of material to be individually removed from each individual blade now becomes $$\mathrm{\Delta }{m}_{\mathit{schaufelebzutragen}}={\mathit{m}}_{\mathit{shovel}}\mathit{-}{\mathit{m}}_{\mathit{schaufelmin}}$$

calculated.

In the following step, the respective amount of material exceeding the smallest blade mass is removed by the individual blades in an etching process, so that all blades have approximately the same thickness, chord length and mass and thus the same natural frequency and thus different blade loads are avoided. The amount of material removed is determined by the etching time and the concentration of the etching solution. The amount of material removed can be checked by interim measurement of the blade internal frequency according to the measurement method mentioned above.

The removal of the material is carried out according to a first embodiment by individually dipping the blade concerned in a trained for a single blade etching or - according to a second, described in the present embodiment variant - by immersion of all blades in a common etching in several successive steps. In this case, the disc and initially only the thinnest blade, in which no removal of material, are protected by a masking before the action of the etching and it is removed in the first etching step of all unmasked blades, the amount of material from the blade with the smallest amount of material to be removed must be removed. After the first etching step, the second blade, reduced to the smallest thickness, is also masked. In the next etching step, the amount of material remaining on the remaining thinnest uncovered blade is removed from the remaining blades. These operations are continued until the mass of the initially thickest blade is reduced by means of the etching solution to the mass of the blade with the lowest initial mass. Between the individual work steps the blade natural frequency and the material removal can be checked again and again.

Finally, the natural frequency of the individual blades is again determined as described above. If matching natural frequencies and masses are found, the process is completed. Otherwise, the above-described etching process is repeated.

The blades of the blisk now have substantially identical properties in terms of mass and natural frequency, so that the maximum blade amplitudes of the blade, which are excited by uneven pressure distribution in the flow channel be avoided in the Blisk design undamped blades and accordingly high blade loads. At the same time caused by different blade masses imbalance of the wheels produced by the method described above is largely eliminated and reduces the imbalance of the impeller as a whole.

According to a third variant, the successive etching described above can also be modified such that the impeller dips into a common etching bath and for each blade the material removal takes place individually on the previously determined lowest reference mass, whereby all parts for which no material removal is to take place are masked become.

Prior to mass production of a plurality of impellers according to the above-described method, a test impeller is fitted with strain gauges on individual preselected blades, mounted, and tested in a trial run on the results of the strain gauges for any blade loading due to amplitude peaks, as may be the vibration behavior of the blades , Applying the high temperature strain gauges to the blade surfaces, here by means of ceramic adhesive, causes an increase in the rigidity of the blade strain gauge dressing and thus an increase in the natural frequency of the particular blade-Dehmnessstreifen-band, resulting in a misinterpretation as a result of checking the test wheel may cause the actual wheel characteristics. The blades of the test rotor selected for the attachment of the strain gauges are therefore additionally reduced in the blade thickness, chord length, and thus also the blade mass and the natural frequency during the etching process described above the Dehnmessstreifen expected deviation from the blade natural frequencies of all other uninstrumentierten blades is compensated and during the test run of the Testblisk all blades have the same natural frequency in spite of attached to individual blades strain gauges and thus the test result is not falsified.

Claims (8)

1. Method for the manufacture of integrally designed rotor wheels for compressors and turbines, especially for gas-turbine engines, in which the rotor wheels, which include a disk with peripherally formed-on rotor blades, are manufactured by conventional shaping methods and the thickness and chord length of the blades are subsequently reduced by chemical processing in an etchant, characterized in that

   - after forming, the natural frequency (f _blade) of each individual blade is measured, and

   - the respective blade mass (m _blade) of the individual blades is determined via the relation existing between the blade natural frequency and the blade mass, and

   - for each blade the difference (Δm _{stock to be removed}) between the respective blade mass and the blade with minimum mass (m _{blade min}.) is determined, and

   - finally the mass difference between the respective blade mass and the blade mass is removed by means of an etchant, so that all blades with minimum blade mass and natural frequency (m _{blade min.}, f _{blade min}) essentially have corresponding masses and natural frequencies.
2. Method in accordance with Claim 1, characterized in that excessive blade mass (Δm _{stock to be removed}) is removed by immersion in an etching solution in dependence of the concentration of the solution and/or the immersion time.
3. Method in accordance with Claim 2, characterized in that the rotor wheel to be treated is completely immersed in the etching solution and that the respectively smallest diverging blade mass is removed from the blades in a sequence of etching operations, with the disk of the rotor wheel and the blade/the blades with the smallest mass being covered by a masking agent protecting the blade portions not to be treated prior to each etching operation,
4. Method in accordance with Claim 2, characterized in that the rotor wheel to be treated is completely immersed in the etching solution, and that from each blade the mass respectively exceeding the smallest blade mass is removed individually in a single etching operation, with the remaining rotor wheel portions being covered by a masking agent during the respective etching operation.
5. Method in accordance with Claim 2, characterized in that the blades are individually immersed in an etching bath adapted to the size of the blade and that the blade mass respectively exceeding the smallest blade mass is removed in a single etching operation.
6. Method in accordance with Claim 1, characterized in that prior to series production of the rotor wheels, a test rotor wheel fitted with strain gauges is subjected to a test run under operating conditions, with the stiffening of the blade and the increase of natural frequency due to the application of the strain gauges is compensated for by increased material removal during the etching of the blade.
7. Method in accordance with Claim 1, characterized in that the natural frequency of the individual blades is measured in a state in which the blade is largely decoupled from the other blades which have been strongly detuned by applying an additional mass, with the blade to be measured being excited by a modal hammer and subsequently the natural frequency (f _blade) being measured contactless using a laser vibrometer.
8. Method in accordance with Claim 1, characterized in that the rotor wheels are manufactured by milling and/or electrochemical machining and/or friction welding.